McMillian was drafted in the first round by the Lakers and was also a first-round pick of the New York Nets of the ABA. He signed with the Lakers and replaced Elgin Baylor at forward during the 1971-72 season, becoming a key member of a team that won 33 games in a row and the NBA title.
After the retirement of Wilt Chamberlain, the Lakers needed a center, so they traded McMillian to the Buffalo Braves after the 1972-73 season for Elmore Smith.